Four of Wellington Zoo's baboons have been put down after a break down in their social structure.
The zoo said in a statement on Saturday the male Hamadryas baboons had been fighting, causing serious injury and increased anxiety.
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Other options, like rehoming, were explored but the zoo ultimately decided it would not work. Zoo chief executive Karen Fifield said the decision was not taken lightly.
"We have an important duty of care to ensure that all animals we care for at the Zoo experience positive welfare and unfortunately for these baboons this is no longer the case," she said in a statement.
"When it comes to a decision like this we need to make a decision before the animals begin to suffer, in this case it is a matter of urgency."
Ms Fifield said baboons are a social primate and the current situation among the group had become untenable.
She told Newshub a number of factors led to the breakdown, including the size of the group and the fact all the baboons were male.
There are now no Hamadryas baboons at Wellington Zoo.
Zoo animal welfare committee member Dr Ngaio Beausoleill said the decision was a difficult one to make, but humane.
"It is Wellington Zoo's responsibility to have the knowledge and experience to do what is best for the animals in their care.
"In this case, as difficult as the decision was, this was the most humane decision for the animals."
Ms Fifield said the zoo staff and community will miss the baboons terribly.